The effect of traditional stir-frying process on hydrophilic and lipophilic antioxidant capacities of pine nut kernels

Abstract

The effect of traditional stir-frying process at different heating temperatures (50–150 °C) and time periods (5–20 min) on hydrophilic part (total and individual phenolics), lipophilic part (tocopherol and phytosterol compounds) and their corresponding antioxidant capacities in pine nut kernels were investigated. The concentrations of total phenolics, phenolic acids, tocopherols and phytosterols in raw pine nut kernels were 15.76 mg gallic acid equivalents/100 g dry weight (mg GAE/100 g DW), 12.15 mg/100 g DW, 28.67 mg/100 g DW and 198.81 mg/100 g DW, respectively. Stir-frying at low temperatures over short time periods led to an increase of phenolics, phytosterols and hydrophiliic antioxidant capacities. However, these values decreased under the longer heating time and the higher temperature. Tocopherols and lipophilic antioxidant capacities did not show clear changes at lower heating temperatures or shorter heating times, while they had an apparent decreasing trend at higher heating temperatures or longer heating times. Gallic acid might be the main component, which is responsible for the hydrophilic antioxidant capacity (R2 = 0.84, 0.81 and 0.81 using DPPH, FRAP and H-ORAC assays), and tocopherols might be the main antioxidant components in the lipophilic part (R2 = 0.87 and 0.89 using DPPH and L-ORAC assays).